The objective of this research is the investigation of the immunopathogenesis of Chlamydia trachomatis infection. This goal is approached through the studies of humoral and cellular immune responses by measurement of serum and local antibodies and lymphocyte transformation in patients with uncomplicated urethral and/or cervical C. trachomatis infection, with local or systemic complications of C. trachomatis infection such as epididymitis, pelvic inflammatory disease, perihepatitis and peritonitis (Fitz-Hugh-Curtis syndrome), or with Reiter's syndrome (urethritis, arthritis, and conjunctivitis); through studies of the nature of successful intracellular parasitism by C. trachomatis in mouse and human monocytic phagocytes; through the in vitro studies of cellular immunity using mouse and human monocytic phagocytes; and through the studies of pathogenesis and immunology of C. trachomatis infection in a murine model system.